The role of GDF15 in attenuating noise-induced hidden hearing loss by alleviating oxidative stress.

Noise-induced hidden hearing loss (HHL) is a newly uncovered form of hearing impairment that causes hidden damage to the cochlea. Patients with HHL do not have significant abnormalities in their hearing thresholds, but they experience impaired speech recognition in noisy environments. However, the mechanisms underlying HHL remain unclear. In this study, we developed single-cell transcriptome profiles of the cochlea of mice with HHL, detailing changes in individual cell types. Our study revealed a transient threshold shift, reduced auditory brainstem response wave I amplitude, and decreased number of ribbon synapses in HHL mice. Our findings suggest elevated oxidative stress and GDF15 expression in cochlear hair cells of HHL mice. Notably, the upregulation of GDF15 attenuated oxidative stress and auditory impairment in the cochlea of HHL mice. This suggests that a therapeutic strategy targeting GDF15 may be efficacious against HHL.

Dexamethasone nanocrystals-embedded hydroxypropyl methylcellulose hydrogel increases cochlear delivery and attenuates hearing loss following intratympanic injection.

Herein, dexamethasone (DEX) nanocrystalline suspension (NS)-embedded hydrogel (NS-G) was constructed using a hydroxypropyl methylcellulose (HPMC) polymer to enhance cochlear delivery and attenuate hearing loss following intratympanic (IT) injection. Hydrophobic steroidal nanocrystals were prepared using a bead milling technique and incorporated into a polysaccharide hydrogel. The NS-G system with HPMC (average molecular weight, 86,000 g/mol; 15 mg/mL) was characterized as follows: rod-shaped drug crystalline; particle size <300 nm; and constant complex viscosity ≤1.17 Pa·s. Pulverization of the drug particles into submicron diameters enhanced drug dissolution, while the HPMC matrix increased the residence time in the middle ear cavity, exhibiting a controlled release profile. The IT NS-G system elicited markedly enhanced and prolonged drug delivery (> 9 h) to the cochlear tissue compared with that of DEX sodium phosphate (DEX-SP), a water-soluble prodrug. In mice with kanamycin- and furosemide-induced ototoxicity, NS-G markedly enhanced hearing preservation across all frequencies (8-32 kHz), as revealed by an auditory brainstem response test, compared with both saline and DEX-SP. Moreover, treatment with NS-G showed enhanced anti-inflammatory effects, as evidenced by decreased levels of inflammation-related cytokines. Therefore, the IT administration of DEX NS-loaded HPMC hydrogels is a promising strategy for treating hearing loss.

Speech intelligibility prediction based on a physiological model of the human ear and a hierarchical spiking neural network.

A speech intelligibility (SI) prediction model is proposed that includes an auditory preprocessing component based on the physiological anatomy and activity of the human ear, a hierarchical spiking neural network, and a decision back-end processing based on correlation analysis. The auditory preprocessing component effectively captures advanced physiological details of the auditory system, such as retrograde traveling waves, longitudinal coupling, and cochlear nonlinearity. The ability of the model to predict data from normal-hearing listeners under various additive noise conditions was considered. The predictions closely matched the experimental test data under all conditions. Furthermore, we developed a lumped mass model of a McGee stainless-steel piston with the middle-ear to study the recovery of individuals with otosclerosis. We show that the proposed SI model accurately simulates the effect of middle-ear intervention on SI. Consequently, the model establishes a model-based relationship between objective measures of human ear damage, like distortion product otoacoustic emissions, and speech perception. Moreover, the SI model can serve as a robust tool for optimizing parameters and for preoperative assessment of artificial stimuli, providing a valuable reference for clinical treatments of conductive hearing loss.

Activated tissue-resident macrophages contribute to hair cell insults in noise-induced hearing loss in mice.

Macrophages serve as the primary immune cell population and assume a pivotal role in the immune response within the damaged cochleae. Yet, the origin and role of macrophages in response to noise exposure remain controversial. Here, we take advantage of Ccr2RFP/+ Cx3cr1GFP/+ dual-reporter mice to identify the infiltrated and tissue-resident macrophages. After noise exposure, we reveal that activated resident macrophages change in morphology, increase in abundance, and migrate to the region of hair cells, leading to the loss of outer hair cells and the damage of ribbon synapses. Meanwhile, peripheral monocytes are not implicated in the noise-induced hair cell insults. These noise-induced activities of macrophages are abolished by inhibiting TLR4 signaling, resulting in alleviated insults of hair cells and partial recovery of hearing. Our findings indicate cochlear resident macrophages are pro-inflammatory and detrimental players in acoustic trauma and introduce a potential therapeutic target in noise-induced hearing loss.

A pore locus in the E1 domain differentially regulates Cx26 and Cx30 hemichannel function.

Connexins (Cxs) function as gap junction (GJ) channels and hemichannels that mediate intercellular and transmembrane signaling, respectively. Here, we investigated the proximal segment of the first extracellular loop, E1, of two closely related Cxs, Cx26 and Cx30, that share widespread expression in the cochlea. Computational studies of Cx26 proposed that this segment of E1 contains a parahelix and functions in gating. The sequence of the parahelix is identical between Cx26 and Cx30 except for an Ala/Glu difference at position 49. We show through cysteine-scanning and mutational analyses that position 49 is pore-lining and interacts with the adjacent Asp50 residue to impact hemichannel functionality. When both positions 49 and 50 are charged, as occurs naturally in Cx30, the hemichannel function is dampened. Co-expression of Cx30 with Cx26(D50N), the most common mutation associated with keratitis-ichthyosis-deafness syndrome, results in robust hemichannel currents indicating that position 49-50 interactions are relevant in heteromerically assembled hemichannels. Cysteine substitution at position 49 in either Cx26 or Cx30 results in tonic inhibition of hemichannels, both through disulfide formation and high-affinity metal coordination, suggestive of a flexible region of the pore that can narrow substantially. These effects are absent in GJ channels, which exhibit wild-type functionality. Examination of postnatal cochlear explants suggests that Cx30 expression is associated with reduced propagation of Ca2+ waves. Overall, these data identify a pore locus in E1 of Cx26 and Cx30 that impacts hemichannel functionality and provide new considerations for understanding the roles of these connexins in cochlear function.

Temporal fine structure sensitivity measured with pulse-spreading harmonic complexes.

Two experiments investigated sensitivity to temporal fine structure (TFS) in a group of normal hearing participants. The stimuli were bandpass filtered pulse-spreading harmonic complexes (PSHCs) with a regular envelope repetition rate and a phase adjusted so that the TFS peaks were progressively shifted across envelope periods. For up-PSHCs, the TFS peaks were advanced, yielding a rising pitch percept, while for down-PSHCs, the peaks were delayed, yielding a falling pitch percept. Experiment 1 showed that in a fixed frequency region, there was a range of rates for which the direction of the pitch change could be identified. Cochlear model simulations suggested that participants may use either place-of-excitation and/or temporal cues to perform this task. Experiment 2 showed that there was an envelope rate below which down-PSHCs and up-PSHCs could not be discriminated. This lower envelope rate limit of TFS sensitivity significantly increased with increases in frequency region and was similar to the lower rate limit of melodic pitch. The results in high frequency regions suggest that TFS cues are available up to 10 kHz when the rank of the lowest component present in the passband is 18, and all harmonics are presumably unresolved.

Two new mouse alleles of Ocm and Slc26a5.

The genes Ocm (encoding oncomodulin) and Slc26a5 (encoding prestin) are expressed strongly in outer hair cells and both are involved in deafness in mice. However, it is not clear if they influence the expression of each other. In this study, we characterise the auditory phenotype resulting from two new mouse alleles, Ocmtm1e and Slc26a5tm1Cre. Each mutation leads to absence of detectable mRNA transcribed from the mutant allele, but there was no evidence that oncomodulin regulates expression of prestin or vice versa. The two mutants show distinctive patterns of auditory dysfunction. Ocmtm1e homozygotes have normal auditory brainstem response thresholds at 4 weeks old followed by progressive hearing loss starting at high frequencies, while heterozygotes show largely normal thresholds until 6 months of age, when signs of worse thresholds are detected. In contrast, Slc26a5tm1Cre homozygotes have stable but raised thresholds across all frequencies tested, 3 to 42 kHz, at least from 4 to 8 weeks old, while heterozygotes have raised thresholds at high frequencies. Distortion product otoacoustic emissions and cochlear microphonics show deficits similar to auditory brainstem responses in both mutants, suggesting that the origin of hearing impairment is in the outer hair cells. Endocochlear potentials are normal in the two mutants. Scanning electron microscopy revealed normal development of hair cells in Ocmtm1e homozygotes but scattered outer hair cell loss even at 4 weeks old when thresholds appeared normal, indicating that there is not a direct relationship between numbers of outer hair cells present and auditory thresholds.

TUBB4B is essential for the cytoskeletal architecture of cochlear supporting cells and motile cilia development.

Microtubules are essential for various cellular processes. The functional diversity of microtubules is attributed to the incorporation of various α- and ß-tubulin isotypes encoded by different genes. In this work, we investigated the functional role of ß4B-tubulin isotype (TUBB4B) in hearing and vision as mutations in TUBB4B are associated with sensorineural disease. Using a Tubb4b knockout mouse model, our findings demonstrate that TUBB4B is essential for hearing. Mice lacking TUBB4B are profoundly deaf due to defects in the inner and middle ear. Specifically, in the inner ear, the absence of TUBB4B lead to disorganized and reduced densities of microtubules in pillar cells, suggesting a critical role for TUBB4B in providing mechanical support for auditory transmission. In the middle ear, Tubb4b-/- mice exhibit motile cilia defects in epithelial cells, leading to the development of otitis media. However, Tubb4b deletion does not affect photoreceptor function or cause retinal degeneration. Intriguingly, ß6-tubulin levels increase in retinas lacking ß4B-tubulin isotype, suggesting a functional compensation mechanism. Our findings illustrate the essential roles of TUBB4B in hearing but not in vision in mice, highlighting the distinct functions of tubulin isotypes in different sensory systems.

Targeting the NLRP3 inflammasome in cochlear macrophages protects against hearing loss in chronic suppurative otitis media.

The activation of the NLRP3 inflammasome has been linked to several inflammatory and autoinflammatory diseases. Despite cases of potential hearing improvement in immune-mediated diseases, direct evidence of the efficacy of targeting this mechanism in the inner ear is still lacking. Previously, we discovered that macrophages are associated with Sensorineural Hearing loss (SNHL) in Chronic Suppurative Otitis Media (CSOM), the leading cause of this permanent hearing loss in the developing world and incurring costs of $4 to $11 billion dollars in the United States. However, the underlying mechanism remained unknown. Here, we investigate how macrophages drive permanent hearing loss in CSOM. We first confirmed the occurrence of NLRP3 inflammasome activation in cochlear macrophages in CSOM. We then revealed that Outer Hair Cells (OHCs) were protected in CSOM by macrophage depletion and subsequently confirmed the same protection in the NLRP3 knockout condition. Furthermore, we showed that therapeutic inhibition of NLRP3 inflammasome activation and downstream inhibition of IL-1ß protects OHCs in CSOM. Collectively, our data demonstrates that the main driver for hearing loss in CSOM is NLRP3 inflammasome activation in cochlear macrophages and this is therapeutically targetable, leading the way for the development of interventions to prevent the leading cause of permanent hearing loss and a costly disease in the developed world.

A cochlear progenitor pool influences patterning of the mammalian sensory epithelium via MYBL2.

During embryonic development, Wnt signaling influences both proliferation and sensory formation in the cochlea. How this dual nature of Wnt signaling is coordinated is unknown. In this study, we define a novel role for a Wnt-regulated gene, Mybl2, which was already known to be important for proliferation, in determining the size and patterning of the sensory epithelium in the murine cochlea. Using a quantitative spatial analysis approach and analyzing Mybl2 loss-of-function, we show that Mybl2 promoted proliferation in the inner sulcus domain but limited the size of the sensory domain by influencing their adjoining boundary position via Jag1 regulation during development. Mybl2 loss-of-function simultaneously decreased proliferation in the inner sulcus and increased the size of the sensory domain, resulting in a wider sensory epithelium with ectopic inner hair cell formation during late embryonic stages. These data suggest that progenitor cells in the inner sulcus determine boundary formation and pattern the sensory epithelium via MYBL2.

Chemokine Receptor CCR2 Is Protective toward Outer Hair Cells in Chronic Suppurative Otitis Media.

Chronic suppurative otitis media (CSOM) is a neglected disease that afflicts 330 million people worldwide and is the most common cause of permanent hearing loss among children in the developing world. Previously, we discovered that outer hair cell (OHC) loss occurred in the basal turn of the cochlea and that macrophages are the major immune cells associated with OHC loss in CSOM. Macrophage-associated cytokines are upregulated. Specifically, CCL-2, an important member of the MCP family, is elevated over time following middle ear infection. CCR2 is a common receptor of the MCP family and the unique receptor of CCL2. CCR2 knockout mice (CCR2-/-) have been used extensively in studies of monocyte activation in neurodegenerative diseases. In the present study, we investigated the effect of CCR2 deletion on the cochlear immune response and OHC survival in CSOM. The OHC survival rate was 84 ± 12.5% in the basal turn of CCR2+/+ CSOM cochleae, compared with was 63 ± 19.9% in the basal turn of CCR2-/- CSOM cochleae (p ≤ 0.05). Macrophage numbers were significantly reduced in CCR2-/- CSOM cochleae compared with CCR2+/+ CSOM cochleae (p ≤ 0.001). In addition, CCL7 was upregulated, whereas IL-33 was downregulated, in CCR2-/- CSOM cochleae. Finally, the permeability of the blood-labyrinth barrier in the stria vascularis remained unchanged in CCR2-/- CSOM compared with CCR2+/+ CSOM. Taken together, the data suggest that CCR2 plays a protective role through cochlear macrophages in the CSOM cochlea.

Effects of Castanopsis echinocarpa on Sensorineural Hearing Loss via Neuronal Gene Regulation.

Sensorineural hearing loss (SNHL), characterized by damage to the inner ear or auditory nerve, is a prevalent auditory disorder. This study explores the potential of Castanopsis echinocarpa (CAE) as a therapeutic agent for SNHL. In vivo experiments were conducted using zebrafish and mouse models. Zebrafish with neomycin-induced ototoxicity were treated with CAE, resulting in otic hair cell protection with an EC50 of 0.49 µg/mL and a therapeutic index of 1020. CAE treatment improved auditory function and protected cochlear sensory cells in a mouse model after noise-induced hearing loss (NIHL). RNA sequencing of NIHL mouse cochleae revealed that CAE up-regulates genes involved in neurotransmitter synthesis, secretion, transport, and neuronal survival. Real-time qPCR validation showed that NIHL decreased the mRNA expression of genes related to neuronal function, such as Gabra1, Gad1, Slc32a1, CaMK2b, CaMKIV, and Slc17a7, while the CAE treatment significantly elevated these levels. In conclusion, our findings provide strong evidence that CAE protects against hearing loss by promoting sensory cell protection and enhancing the expression of genes critical for neuronal function and survival.

[The imaging appearances of stapical footplate fistula related to inner ear malformation].

Objective: To summarize the HRCT and MRI appearances of stapical footplate fistula related to inner ear malformation (SFF-Re-IEM). Methods: The HRCT and MRI materials of 48 cases (53 ears) SFF-Re-IEM were retrospectively analyzed. Among them, 25 SFF-Re-IEM ears were confirmed by surgery. Their CT and MRI findings including associated IEM type, internal auditory canal (IAC) malformation, tympanic fluid, its density and signal features, and accompanied labyrinthitis were recorded. Results: Among 48 cases (53 ears) with SFF-Re-IEM, 17 ears with incomplete partition type Ⅰ, accounting for 32.1%, 13 ears with common cavity for 24.5%, 13 ears with cochlear aplasia for 24.5%, 7 ears with cochlear dysplasia Ⅱ for 13.2%, and 3 ears with Mondini for 5.7%,were found respectively. 94.3% of them were associated with a defect or dysplasia in the found of the IAC. They were divided into 4 types according to the intact of the stapical footplate and accompanied CSF otorrhea: 22 ears were diagnosed as the stapical footplate leaking, of them, 2 ears might come from the stapical footplate bony defect, 6 ears were from the stapical footplate hernia. 1 ear belonged to the peristapical footplate leaking. 30 ears with the isolated the stapical footplate hernia were another found. The bony defect in 2 ears with the stapical footplate bony defect were not presented on CT and MRI.The focal bony defect of the affected stapical footplate of 36 ears with the stapical footplate hernia were demonstrated, which presented the hemispherical protruding into the tympana, the soft-tissue density on CT, and CSF-like signal on the MR heaved-T2WI images. Among 22 ears with the stapical footplate leaking, their imaging appearances varied from the different amount of the leaking CSF. Besides the focal bony defects of the affected stapical footplates, there were much more CSF-like density or signal in the ipsilateral tympanic cavity in 17 affected ears connecting with the vestibule through the defect area. In the CSF leaking ears with less CSF leaking in 5 ears, the CSF-like cysts like SFH were shown on the stapical footplate defect area, but their outer edges were irregular, and the CSF-like signal scattering in the tympanic cavity did not connect with the protruding cysts at the stapical area. Conclusion: The variable appearances of the SFF-Re-IEM ears based on the different subtypes are its characteristic HRCT and MRI appearances. This is helpful for the SFF-Re-IEM diagnosing to grasp its imaging features.

Microneedle-Mediated Delivery of siRNA via Liposomal-Based Transfection for Inner Ear Gene Therapy.

HYPOTHESIS: Microneedle-mediated intracochlear injection of siRNA-Lipofectamine through the round window membrane (RWM) can be used to transfect cells within the cochlea. BACKGROUND: Our laboratory has developed 100-µm diameter hollow microneedles for intracochlear injection through the guinea pig RWM. In this study, we test the feasibility of microneedle-mediated injection of siRNA and Lipofectamine, a commonly used reagent with known cellular toxicity, through the RWM for cochlear transfection. METHODS: Fluorescently labeled scramble siRNA was diluted into Lipofectamine RNAiMax and OptiMEM. One microliter of 5 µM siRNA was injected through the RWM of Hartley guinea pigs at a rate of 1 µl/min (n = 22). In a control group, 1.0 µl of Lipofectamine, with no siRNA, was diluted into OptiMEM and injected in a similar fashion (n = 5). Hearing tests were performed before and either at 24 hours, 48 hours, or 5 days after injection. Afterward, animals were euthanized, and cochleae were harvested for imaging. Control cochleae were processed in parallel to untreated guinea pigs. RESULTS: Fluorescence, indicating successful transfection, was observed within the basal and middle turns of the cochlea with limited distribution in the apex at 24 and 48 hours. Signal was most intense in the organ of Corti, spiral ligament, and spiral ganglion. Little to no fluorescence was observed at 5 days post-injection. No significant changes in auditory brainstem response (ABR) were noted post-perforation at 5 days, suggesting that siRNA-Lipofectamine at low doses does not cause cochlear toxicity. CONCLUSIONS: Small volumes of siRNA and Lipofectamine can be effectively delivered to cochlear structures using microneedles, paving the way for atraumatic cochlear gene therapy.

Protective Effect of Memantine on Cisplatin-Induced Ototoxicity: An In Vitro Study.

HYPOTHESIS: Memantine, an N -methyl- d -aspartate receptor antagonist, is widely used to treat Alzheimer's disease and has been found to have potential neuroprotective effects. In this study, we evaluated the protective effects of memantine against cisplatin-induced ototoxicity. BACKGROUND: Cisplatin is a widely used anticancer drug for various cancers; however, its use is limited by its side effects, including ototoxicity. Several drugs have been developed to reduce cisplatin toxicity. In this study, we treated cisplatin-damaged cochlear hair cells with memantine and evaluated its protective effects. METHOD: House Ear Institute Organ of Corti 1 (HEI-OC1) cells and cochlear explants were treated with cisplatin or memantine. Cell viability, apoptotic patterns, reactive oxygen species (ROS) production, Bcl-2/caspase-3 activity, and cell numbers were measured to evaluate the anti-apoptotic and antioxidative effects of memantine. RESULT: Memantine treatment significantly improved cell viability and reduced cisplatin-induced apoptosis in auditory cells. Bcl-2/caspase-3 activity was also significantly increased, suggesting anti-apoptotic effects against cisplatin-induced ototoxicity. CONCLUSION: Our results suggest that memantine protects against cisplatin-induced ototoxicity in vitro, providing a potential new strategy for preventing hearing loss in patients undergoing cisplatin chemotherapy.

Pesticide metabolite 3, 5, 6-trichloro-2-pyridinol causes massive damage to the cochlea resulting in hearing loss in adult mice.

Pesticides are a group of extensively used man-made chemicals with high toxicity and strong residues, which are closely related to hearing health. Pesticide metabolite 3, 5, 6-Trichloro-2-pyridinol (TCP) exposure leads to neurotoxicity and auditory cell toxicity. However, whether TCP causes damage to hearing in adult mice is not clear. In this study, adult male C57BL/6 mice continuously exposed to TCP for 21 days showed a dose-dependent elevation of hearing threshold. Outer hair cells and spiral neuron cells were lost in a dose-dependent manner. Type I and V of spiral ligament were severely shrunk and stria vascularis were thinned in mice after 50 and 150 mg/kg TCP exposure. Similarly, ROS levels in the cochlea were significantly increased whereas the activities of anti-oxidation enzymes were decreased after TCP exposure. The expression level of Na+/K+ ATPase was decreased, resulting in cochlear potential disruption. Levels of inflammatory factors (TNF-α and IL-1ß), γ-H2AX, and pro-apoptotic-related factors (Bax and cleaved-Caspase 3) were elevated, respectively. These results suggest that TCP can cause oxidative stress, inflammation, and imbalance of cochlear potential in the cochlea, induce cochlear DNA damage and apoptosis, and cause cochlear morphological changes, eventually leading to impaired hearing function.

Development of a drug delivering round window niche implant for cochlear pharmacotherapy.

BACKGROUND: There exists an unfulfilled requirement for effective cochlear pharmacotherapy. Controlled local drug delivery could lead to effective bioavailability. The round window niche (RWN), a cavity in the middle ear, is connected to the cochlea via a membrane through which drug can diffuse. We are developing individualized drug-eluting RWN implants (RNIs). To test their effectiveness in guinea pigs, a commonly used model in cochlear pharmacology studies, it is first necessary to develop guinea pig RNIs (GP-RNI). METHODS: Since guinea pigs do not have a RWN such as it is present in humans and to reduce the variables in in vivo studies, a one-size-fits-all GP-RNI model was designed using 12 data sets of Dunkin-Hartley guinea pigs. The model was 3D-printed using silicone. The accuracy and precision of printing, distribution of the sample ingredient dexamethasone (DEX), biocompatibility, bio-efficacy, implantability and drug release were tested in vitro. The GP-RNI efficacy was validated in cochlear implant-traumatized guinea pigs in vivo. RESULTS: The 3D-printed GP-RNI was precise, accurate and fitted in all tested guinea pig RWNs. DEX was homogeneously included in the silicone. The GP-RNI containing 1% DEX was biocompatible, bio-effective and showed a two-phase and sustained DEX release in vitro, while it reduced fibrous tissue growth around the cochlear implant in vivo. CONCLUSIONS: We developed a GP-RNI that can be used for precise inner ear drug delivery in guinea pigs, providing a reliable platform for testing the RNI's safety and efficacy, with potential implications for future clinical translation.

Cochlear Implantation: Small Cochlear Diameter May Indicate Degree of Abnormality.

Cochlear size variation was first reported in 1884, and since then, there have been various reports confirming the same. Yet, there is no single report that has displayed the wide variations in the cochlear size in a single layout capturing the cochlea in the oblique coronal view/ cochlear view. Basal turn diameter (A-value) was measured in the oblique coronal plane using the OTOPLAN® otological preplanning tool in 104 computed tomography (CT) scans of the temporal bones of cochlear implant (CI) recipients in a tertiary CI center. All CT scans with an image resolution of at least 0.5 mm and identified as having cochleae with normal anatomy were included in this study. A 3-dimensional (3D) segmentation was performed using the 3D slicer and visualized to evaluate the impact of cochlear size on the number of turns studied. The A-value was found to vary between 7.3 mm and 10.4 mm among the studied patients. Three-dimensional segmentation of the inner ear revealed only 2 turns of the cochlea in 4 ears, with A-values of 7.3, 8.8, 7.8, and 7.7 mm. One ear had only 11 /2 turns of the cochlea, with an A-value of 7.9 mm. As a further advancement in the assessment of cochlear size as determined by the A-value, 3D segmentation of the complete inner ear provides a full picture of the number of cochlear turns. Three-dimensional segmentation of the entire inner ear could help improve the preoperative planning of CI surgery and have implications for electrode array selection. Cochlear size could be a predictor of the number of cochlear turns, even in cases that look normal from the radiological findings. The findings of this study could help in improving the preoperative planning for a more successful CI surgery by differentiating between the normal and abnormal cochlea.

The Impact of Oleuropein on Cisplatin-Induced Toxicity in Cochlear Cells in Relation to the Expression of Deoxyribonucleic Acid Damage-Associated Genes.

Different organs respond differently to cisplatin (CDDP)-induced toxicity. Oleuropein (OLE) is a natural phenolic antioxidant. The purpose of this study was to determine the potential protective effect of OLE against CDDP-induced ototoxicity by evaluating expression of genes associated with deoxyribonucleic acid (DNA) damage and repair in cochlear cells. House Ear Institute-Organ of Corti 1 (HEI-OC1) cells were treated using CDDP, OLE, and OLE-CDDP. The water-soluble tetrazolium salt assay was used for monitoring cell viability. Deoxyribonucleic acid damage in cells due to the CDDP, OLE, and combination treatments was determined using a flow-cytometric kit. The change in the expression of 84 genes associated with CCDP, OLE, and OLE-CDDP treatments that induced DNA damage was tested using the reverse transcription polymerase chain reaction array. Changes ≥3-fold were considered significant. House Ear Institute-Organ of Corti 1 cell viability was significantly reduced by CDDP. The OLE-CDDP combination restored the cell viability. Cisplatin increased the H2AX ratio, while OLE-CDDP combination decreased it. Some of the DNA damage-associated genes whose expression was upregulated with CDDP were downregulated with OLE-CDDP, while the expression of genes such as Gadd45g and Rev1 was further downregulated. The expression of DNA repair-related Abl1, Dbd2, Rad52, and Trp53 genes was downregulated with CDDP, whereas their expression was upregulated with OLE-CDDP treatment. In cochlear cells, the OLE-CDDP combination downregulated DNA damage-associated gene expression relative to that upregulated mainly by CDDP. The results revealed that OLE has a potential protective effect on CDDP-induced ototoxicity in cochlear cells by altering the expression of DNA damage-related genes.